Fluid power regenerator

ABSTRACT

A regenerator for a fluid power system is arranged to control flow rates while converting pressure drops accompanying resulting changes in flow rates into useful work. A gang of displacers are incorporated into a fluid flow network that also includes an array of selectable flow paths through the displacers. A control system, responsive to changes in demand for the flow of fluid, selects among the flow paths to operate the displacers in various combinations as motors, pumps, and recirculators for dividing the flow of fluid into two variably sized portions. One portion of the flow is sized to match the demand for fluid flow, and the other portion of the flow is converted into useful work.

TECHNICAL FIELD

My invention relates to the field of fluid power systems and, inparticular, to such systems incorporating fixed displacement pumps ormotors.

BACKGROUND

Most energy losses from fluid power systems occur as a result ofdecreases in fluid pressure that do not accomplish useful work. Suchpressure drops dissipate energy expended to pressurize the fluid in theform of heat.

For example, fixed displacement pumps are generally sized to meet amaximum system demand for a rate of fluid flow at a given pressure eventhough the maximum demand occurs only rarely. Any portion of thepressurized flow that is not required to meet a particular demand isexhausted to a return side of the fluid system by a pressure controlrelief valve, whose primary function is to limit system pressure. Aproduct of the volume of exhausted fluid and its drop in pressure equalsthe amount of energy that is lost through the relief valve.

Similar energy losses are associated with fixed displacement motors thatconvert fluid power in the form of flow rate and pressure intomechanical power in the form of rotational speed and torque. Flowcontrol valves, whose primary function is to control flow rate, areoften used as throttle valves to regulate the rotational speed of fixeddisplacement motors. However, if a pressure drop across the motor(corresponding to a particular output torque of the motor) is less thanthe system pressure, then a second pressure drop equal to the differencepressure occurs across the throttle valve. The amount of energy lost isequal to a product of the volume of fluid passing through the throttlevalve and the drop in pressure across the valve.

Many different approaches have been taken to minimize energy lossesassociated with fixed displacement pumps and motors. One approach tominimizing such energy losses is to control the rotational speed of aprime mover driving the fixed displacement pump as a function of systempressure. Electrical energy used to power an electric motor as the primemover is saved by reducing the rotational speed of the electric motor inresponse to an increase in system pressure. However, this approach hasbeen limited mainly to small electric motors as prime movers, becauselarge electric motors are more difficult to operate efficiently atvarying speeds and react much more slowly to desired changes in speed.

Another approach to energy savings with fixed displacement pumps andmotors has been to replace single fixed displacement pumps and motorswith respective gangs of smaller fixed displacement pumps and motorshaving the same total displacement. For example, U.S. Pat. No. 4,199,943to Hunt discloses a fluid pumping system in which a gang of fixeddisplacement pumps are driven in unison by a prime mover. The pumps drawfluid from a common reservoir and output the fluid through respectivediverter valves to either a motor supply line or the reservoir. Thediverter valves are biased into positions that connect each of the pumpsto the motor supply line. However, the diverter valves are controlled tosuccessively divert the pump output flow to the reservoir in response topressure increases in the motor supply line.

U.S. Pat. No. 4,245,964 to Rannenberg saves energy in a similar mannerby mechanically connecting a pair of fixed displacement pumps to acommon prime mover and deactivating one of the pumps in response to anincrease in system pressure. However, instead of exhausting output flowfrom the deactivated pump to a reservoir, the output flow isrecirculated through the deactivated pump so that there is no pressuredifferential across the pump.

The pumping systems of both Hunt and Rannenberg can be used to saveenergy by better matching power demands on the prime mover with powerexpended by the fluid power system to accomplish useful work. Moreparticularly, both systems save energy by better matching the effectivedisplacements of their pump systems to demands for fluid flow at givenpressures. However, the effective displacements of their pump systemscan be varied only by large increments, and power is wasted when thedemand for fluid flow cannot be exactly matched by the availableincrements of displacement.

Fluid transmissions have also been arranged in a similar manner toconserve power. For example, U.S. Pat. No. 986,780 to Sundh and U.S.Pat. Nos. 2,370,526 and 2,374,588 to Doran disclose fluid transmissionsin which respective gangs of fixed displacement motors are connected tocommon output shafts. Each of the transmissions includes a fixeddisplacement pump that provides a source of fluid flow to the gang ofmotors and one or more valves that provide for successively connectingthe motors to the fluid flow. Output torque of the transmissionincreases and output rotational speed decreases as more of the motorsare connected.

Although such fluid transmissions are operable over a wide range ofoutput speeds while delivering most of the available fluid power to aload, the actual output speed must be controlled by other means.However, if the output speed is controlled (e.g., by limiting the flowrate through the transmission with a throttle valve), then less than allof the available fluid power may be delivered by the transmission (e.g.,the pressure drop across the transmission is less than the systempressure) and the unused power may be wasted. In other words, energylosses from transmissions including respective gangs of fixeddisplacement motors are similar to losses from individual fixeddisplacement motors when less than all of the available fluid power isdelivered by the transmissions or individual motors.

The attempts to reduce energy losses from fluid power systems alsoinclude replacing fixed displacement pumps and motors with variabledisplacement pumps and motors. However, with respect to fixeddisplacement pumps and motors, variable displacement pumps and motorsare larger, more expensive, less reliable, and more sensitive to fluidcontaminants; require more maintenance; and are subject to catastrophicfailure that can do far-ranging damage to the fluid system in which theyare used. Fixed displacement pumps and motors, such as gear pumps andmotors, wear in a very gradual and predictable manner that is easilymonitored by their performance in conducting routine maintenance orreplacement.

Variable displacement pumps and motors have also been used to supplementoperations of fixed displacement pumps and motors to reduce energylosses. For example, U.S. Pat. No. 3,038,312 to Marsh discloses ahydrostatic transmission in which a device operable as either a variabledisplacement pump or a variable displacement motor is mechanicallycoupled to a fixed displacement pump driven by a prime mover. As a pump,the variable displacement device supplements the operation of the fixeddisplacement pump by delivering variable amounts of additional flow to afixed displacement motor. However, when the motor's demand for fluidflow is less than the output flow of the fixed displacement pump, thevariable displacement device is operated as a motor that receivesvariable amounts of the flow from the fixed displacement pump andcontributes to the pump's rotation.

The variable displacement device of Marsh operating as a motor replacesa conventional throttle valve interrupting a motor by-pass line forcontrolling the rotational speed of a fixed displacement motor in ahydrostatic transmission. That is, the variable displacement device(motor) of Marsh provides a conventional throttling function, but alsoconverts a pressure drop across the variable displacement motor intouseful work by turning the fixed displacement pump. Energy reclaimedfrom the pressure drop is used to reduce input power demands of theprime mover. The use of a pressure drop, which would otherwise result ina loss of energy from a fluid system, to accomplish useful work isreferred to as "regeneration".

A similar type of regeneration is achieved in a hydrostatic transmissiondisclosed in U.S. Pat. No. 3,203,185 to Williams by replacing acounterbalance pressure control valve in a return line of thetransmission with a variable displacement pump. Ordinarily, such acounterbalance valve would be used to maintain a predeterminedbackpressure in the return line to prevent variations in a load fromoverdriving an output shaft of the transmission. However, a pressuredrop across the counterbalance valve dissipates a large amount of energyrequired to pressurize the fluid as heat.

In place of the counterbalance valve, Williams connects the variabledisplacement pump between an output port of a fixed displacement motorthat drives the transmission output shaft and an input port of a fixeddisplacement pump that provides a source of fluid flow. The variabledisplacement pump is driven by the fixed displacement motor through acommon mechanical connection with the output shaft, and the pump'sdisplacement is varied to maintain a predetermined pressure in thereturn line to the fixed displacement pump. The pressurized fluid in thereturn line provides the fixed displacement pump with a supply of fluidthat reduces the amount of energy required by the fixed displacementpump to raise the pressure of the fluid to system pressure. In otherwords, the differential pressure across the fixed displacement pump isreduced by the backpressure.

U.S Pat. No. 2,549,989 to Simonds discloses a multiple motor fluidtransmission system that also achieves regenerative effects by couplingvariable displacement devices to each of three fixed displacementmotors. A primary variable displacement pump driven by a prime moverprovides a supply of fluid at a constant pressure to each of the fixeddisplacement motors and to each of the variable displacement devicesthat are respectively coupled to the motors.

When a load exceeds the torque capacity of one of the motors, theassociated variable displacement device is arranged to function as amotor for supplementing the torque output of the fixed displacementmotor. However, when the torque capacity of one of the motors exceedsthe requirements of a load, the associated variable displacement deviceis arranged to function as a pump for using the excess capacity of thefixed displacement motor to add to the supply of pressurized fluid. Inother words, if the pressure drop across one of the fixed displacementmotors is less than the system pressure, the remaining pressure is usedto drive a variable displacement pump that returns part of the flow fromthe motor to system pressure. The increased flow of pressurized fluidreduces the demand for fluid flow from the primary variable displacementpump supplying the system.

The regenerative fluid systems of Marsh, Williams, and Simonds saveenergy by using variable displacement devices in place of throttlevalves or relief valves for converting pressure drops in their systemsinto useful work. Although possibly smaller than stand-alone variabledisplacement pumps and motors, the known variable displacement devicesthat are mechanically connected to fixed displacement pumps or motorsfor regenerative purposes have the same disadvantages as stand-alonevariable displacement pumps and motors. Accordingly, the knownregenerative systems have limited practical applications.

SUMMARY OF INVENTION

My invention, which may be generally referred to as a "fluid powerregenerator", involves a gang of at least two displacers that areincorporated into a fluid flow network to at least partially replace thefunctions of valves or other devices for regulating pressure or flowrate in fluid power systems. The displacers, which are individuallyoperable as fixed displacement pumps or motors, control flow rate whileconverting pressure drops accompanying resulting changes in the flowrate into useful work.

The displacers are mechanically connected to each other for displacingrespective portions of a flow of fluid and are incorporated into a fluidflow network that also includes an array of selectable flow pathsthrough the displacers. A control system, responsive to changes indemand for the flow of fluid, selects among the flow paths to transformvarying portions of the flow of fluid into mechanical power conveyedbetween the displacers.

The fluid flow network divides the flow of fluid into two portions. Oneportion of the flow of fluid is at least approximately sized to match aparticular demand for the flow of fluid. The other portion of the flowof fluid is managed so that any pressure drop accompanying the divisionof the flow of fluid is converted into useful work. For example, excessflow of fluid is transformed into mechanical power by using the excessflow to drive at least one of the displacers as a motor. The mechanicalpower generated by one of the displacers operating as a motor is used todrive at least one other of the displacers as a pump.

My fluid power regenerator is especially suitable for use in conjunctionwith fixed displacement pumps or motors or in place of variabledisplacement pumps and motors. Each of these uses has at least onedifferent basic configuration. A first of the basic configurations isused in conjunction with a fixed displacement pump, and a second of thebasic configurations is used as a replacement for a variabledisplacement pump. Both the first and the second basic configurations ofmy regenerator limit system pressure by exhausting excess fluid flow toa return side of the system. A third of the basic configurations is usedin conjunction with a fixed displacement motor or similar actuator(e.g., piston actuator), and a fourth of the basic configurations isused as a replacement for a variable displacement motor. Both the thirdand fourth basic configurations exhaust excess fluid flow to controloutput speed or torque (or force) imparted to a load by a motor (orother actuator). However, all four of the basic configurations convertthe excess flow into useful work before exhausting the excess flow to areservoir or other store of fluid including a return side of the fluidpower system.

The first basic configuration of my fluid regenerator is arranged with agang of displacers that are mechanically interconnected with each otherfor dividing a flow of fluid from a fixed displacement pump intopredetermined proportions. The displacers are incorporated into a fluidflow network that includes: a first pressure line for connectingrespective input ports of the displacers to an output port of the fixeddisplacement pump, a second pressure line for connecting respectiveoutput ports of the displacers to a load, and a return line forconnecting the output port of one or more of the displacers to areservoir (or return side of the fluid system). A control system,responsive to a reduced demand for the flow of fluid in the secondpressure line, provides for diverting fluid flowing out of the one ormore displacers from the second pressure line to the return line.

The displacers interconnecting the first pressure line and the returnline function as motors, and other of the displacers interconnecting thefirst and the second pressure lines function as pumps. The displacersoperating as motors transform a portion of the flow of fluid that is notrequired to satisfy the demand for fluid flow to the load intomechanical power that is used to drive the other displacers as pumps.The first pressure line connects the gang of displacers in series withthe fixed displacement pump, and the displacers operating as pumps helpto relieve demand on a prime mover driving the fixed displacement pumpto more closely match the demand for fluid flow to the load.

The fluid flow network preferably includes at least three displacers(incorporated into a fluid flow network as described above) and afeedback line for connecting an output port of a third displacer to thefirst pressure line. The control system further provides for divertingfluid flowing out of the third displacer from the second pressure lineto either the return line or the feedback line. Diverting the outputflow from the third displacer to the feedback line recirculates a fixedvolume of fluid through the third displacer; and this effectivelyremoves the third displacer from the flow of fluid, which is thereafterdivided among the remaining displacers. Displacers operating in arecirculating mode are hereinafter referred to as "recirculators". Thechoice of operating the displacers as pumps, motors, or recirculatorsenables my regenerator to more closely match the demand for fluid flowto the load with the demand on the prime mover required to drive thefixed displacement pump.

This configuration of my regenerator can be used to limit pressureincreases in the second pressure line to the load in response to areduced demand for fluid flow from the fixed displacement pump. Theexcess capacity of the fixed displacement pump is routed through thedisplacers to reduce pressure in the first pressure line between thefixed displacement pump and the displacers. The reduction in outputpressure of the fixed displacement pump saves energy by reducing powerdemands on the prime mover driving the fixed displacement pump.

The second basic configuration of my regenerator (which replaces avariable displacement pump) is arranged with a gang of displacers thatare mechanically interconnected with each other and with a prime moverfor displacing predetermined proportions of a flow of fluid. Thedisplacers are incorporated into a fluid flow network that includes: anintake line for connecting respective input ports of the displacers to areservoir, a pressure line for connecting respective output ports of thedisplacers to a load, a feedback line for connecting the pressure lineto the input port of one or more of the displacers, and a return linefor connecting the output port of the one or more displacers to thereservoir. A control system, responsive to a reduced demand for fluidflow in the pressure line, provides for diverting fluid flowing into theone or more displacers from the intake line to the feedback line and fordiverting fluid flowing out of the one or more displacers from thepressure line to the return line.

The displacers interconnecting the feedback line and the return line aredriven as motors for helping to drive other displacers interconnectingthe intake line and pressure line as pumps. However, the one or moredisplacers can also be operated as recirculators by interconnectingeither the intake and return lines or the feedback and pressure lines.Fluid flow through the displacers operating as either motors orrecirculators reduces demand on the prime mover. The displacersoperating as motors subtract from the displacement of the displacersoperating as pumps. However, the displacers operating as recirculatorsneither add to nor subtract from the pumping displacement. The choice ofoperating the displacers as pumps, motors, or recirculators enables thisconfiguration of my regenerator to more closely match demand of the loadwith the demand on the prime mover required to drive the gang ofdisplacers.

The third basic configuration of my regenerator, which is used inconjunction with a fixed displacement actuator, is arranged with a gangof displacers that are mechanically interconnected with each other fordividing a flow of fluid into predetermined proportions. However,similar to a throttle valve, the fluid flow network can be arranged tocontrol flow rates either to or from a fixed displacement actuator. Forcontrolling flow rates to the actuator (also referred to as "meter in"),the fluid flow network includes: a first pressure line for connectingrespective input ports of the displacers to a source of the fluid flow,such as a primary pump; a second pressure line for connecting respectiveoutput ports of the displacers to an input port of the actuator; and areturn line for connecting the output port of one or more of thedisplacers to a reservoir. A control system, responsive to a signal forcontrolling fluid flow through the actuator, provides for divertingfluid flowing out of the one or more displacers from the pressure lineto the return line.

The displacers interconnecting the first pressure line and the returnline function as motors, driving other displacers interconnecting thefirst and the second pressure lines as pumps. The displacers operatingas motors transform a portion of the fluid flow that is not required tosatisfy the demand for fluid flow by the actuator into mechanical powerthat is used to drive the other displacers as pumps. Although anydiversion of the fluid flow to the return line decreases the rate offluid flow to the actuator, the displacers driven as pumps can be usedto increase pressure in the second pressure line to the actuator withrespect to system pressure in the first pressure line.

However, for controlling flow rates from the actuator (also referred toas "meter out"), the fluid flow network includes: a pressure line forconnecting an input port of the actuator to a source of the fluid flow,such as a primary pump; an exhaust line for connecting an output port ofthe actuator to respective input ports of the displacers; a return linefor connecting respective output ports of the displacers to a reservoir;and a feedback line for connecting the output port of one or more of thedisplacers to the pressure line. A control system, responsive to asignal for controlling fluid flow through the actuator, provides fordiverting fluid flowing out of the one or more displacers from thereturn line to the feedback line.

The displacers interconnecting the exhaust line and the return linefunction as motors, and the displacers interconnecting the exhaust lineand the feedback line function as pumps. The displacers operating asmotors transform any remaining portion of the fluid power exhausted fromthe actuator into mechanical power that is used to drive the otherdisplacers as pumps. Fluid flow from the displacers operating as pumpscan be combined with the flow of fluid from the primary pump to theactuator or diverted by a so-called "power beyond" circuit to anotherfluid power system. An intake line connecting the input port of theactuator to the reservoir can also be added so that the gang ofdisplacers can be controlled to extract useful work from a brakingresistance to movement of the actuator. The fluid flow network can alsobe arranged to operate one or more of the displacers as a recirculatorto provide further control over the actuator.

The fourth basic configuration of my regenerator (which replaces avariable displacement motor) is arranged with a gang of displacers thatare mechanically interconnected with each other and with a load fordisplacing predetermined proportions of a flow of fluid. The displacersare incorporated into a fluid flow network that includes: a pressureline for connecting respective input ports of the displacers to a sourceof fluid flow such as a primary pump, a return line for connectingrespective output ports of the displacers to a reservoir, an intake linefor connecting the input port of one or more of the displacers to thereservoir, and a feedback line for connecting the output port of the oneor more displacers to the pressure line. A control system, responsive toa signal for controlling fluid flow through the actuator, provides fordiverting fluid flowing into the one or more displacers from thepressure line to the intake line and for diverting fluid flowing out ofthe one or more displacers from the return line to the feedback line.

The displacers interconnecting the pressure line and the return linefunction as motors, and the displacers interconnecting the intake lineand the feedback line function as pumps. The displacers operating asmotors drive the load as well as the other displacers operating aspumps. One or more of the displacers can also be operated as arecirculator by connecting the displacer between the intake and returnlines. The control system and the fluid flow network control theoperation of the displacers so that most of any fluid flow not requiredto drive the load is converted into useful work.

All four of the basic configurations of my regenerator are preferablyarranged to include respective gangs of displacers that have differentsize displacers to more exactly divide a fluid flow between the portionthat is sized to match a particular demand and the remaining portionthat is converted into useful work. The control system enables thedifferent size displacers to be operated in various combinations ofmotors, pumps, and recirculators to provide, a large number ofproportional changes in the division of fluid flow. For example, thedisplacers in each gang are preferably sized to provide a large numberof useful permutations that include desired incremental divisions of thefluid flow.

More than one gang of displacers can be connected in series within thefluid flow network to adapt my regenerator to a variety of system sizes.For example, a first gang of displacers can be arranged to divide a flowof fluid into a small number of increments. A second gang of displacerscan be arranged to further divide one of the increments of fluid flowthrough the first gang of displacers into a much larger number ofincrements. Thus, the total number of increments into which the fluidflow is divided is equal to a product of the numbers of increments intowhich the fluid is divided by the respective gangs of displacers.Different rates of fluid flow can be accommodated by replacingdisplacers in the first gang of displacers with different sizedisplacers. The second gang of displacers can be standardized for usewith a variety of different size fluid systems.

DRAWINGS

FIG. 1 is a diagram of my regenerator used in conjunction with a fixeddisplacement pump.

FIG. 2 is a diagram of my regenerator used as a replacement for avariable displacement pump.

FIG. 3 is a diagram of my regenerator used in conjunction with a fixeddisplacement motor.

FIG. 4 is a diagram of my regenerator used as a replacement for avariable displacement motor.

FIG. 5 is a diagram of a more detailed version of my regenerator shownin FIG. 1 including two gangs of displacers that are connected in seriesfor adapting my regenerator to different size systems.

FIG. 6 is a diagram of a novel electronic control system speciallyadapted to the embodiment of FIG. 5.

FIG. 7 is a diagram of a novel fluid-powered control system speciallyadapted to the embodiment of FIG. 5.

DETAILED DESCRIPTION

Although my regenerator is preferably constructed with a gang of fourdisplacers as shown in FIG. 5, the different basic configurations of myregenerator can be more easily explained with reference to thesimplified embodiments of FIGS. 1-4 in which the displacers are shown inpairs.

FIG. 1 illustrates my regenerator as part of a fluid pumping system forsupplying a flow of fluid at a constant pressure to a load or at adifferential pressure that exceeds pressure requirements of the load bya constant amount. The system includes a fixed displacement pump 10driven by a prime mover 12 such as an electric motor. An intake line 14connects an input port 16 of pump 10 with a vented reservoir 18. Aprimary pressure line 20, extending from an output port 22 of the pump10, branches into two secondary pressure lines 24 and 26 that form thebeginnings of a fluid flow network of my regenerator.

The secondary pressure line 24 extends through a check valve 28 to asystem output line 30 for supplying a flow of fluid to a load (notshown). The secondary pressure line 26 connects the primary pressureline 20 to respective input ports 32 and 34 of displacers 36 and 38,which are rotatively coupled to each other. The displacers 36 and 38 arepreferably fixed displacement gear drives that can be used as eitherpumps or motors.

Tertiary pressure lines 40 and 42 connect respective output ports 44 and46 of the displacers 36 and 38 to the system output line 30 throughrespective check valves 48 and 50. Secondary return lines 52 and 54,interrupted by respective shutoff valves 56 and 58, connect therespective tertiary pressure lines 40 and 42 to a primary return line 60that empties into reservoir 18. The shutoff valves 56 and 58 are biasedto open positions (as a protection against system damage accompanying anelectrical failure) but can be switched to closed positions byrespective solenoid actuators.

Although it remains a good practice to protect the fixed displacementpump 10 with a pressure relief valve (not shown), my regenerator isintended to at least supplement operation of such a relief valve toconvert its pressure relief function into useful work. A controller 62,which preferably includes a microprocessor and drivers for the solenoidactuators, can be arranged to receive information from a pressure sensor64 for monitoring fluid pressure in the system output line 30. Insteadof dumping a portion of the fluid flow directly to the reservoir 18 inresponse to monitored pressures that exceed a predetermined systempressure, one or the other of the shutoff valves 56 and 58 is allowed toopen for routing the excess fluid flow through one of the displacers 36and 38 before emptying the fluid into the reservoir.

For example, FIG. 1 depicts operation of my regenerator with the valve56 in an open position and the valve 58 actuated to a closed position.Excess fluid flow is directed through the displacer 36 from thesecondary pressure line 26 to the secondary return line 52 and drivesthe displacer 36 as a motor. Mechanical power generated by the displacer36 operating as a motor drives the displacer 38 as a pump in series withthe fixed displacement pump 10. The displacer 38 operating as a pumpproduces, between secondary pressure line 26 and tertiary pressure line40, a pressure differential that reduces fluid pressure in the secondarypressure line 26 as well as in the primary pressure line 20.

The reduction in fluid pressure in the primary pressure line 20 reflectsa reduction in the output pressure of the fixed displacement pump 10.Since fluid power is calculated as a product of pressure and flow rate,the reduction in output pressure of the fixed displacement pump resultsin a corresponding reduction in power demand on the prime mover 12.Thus, energy is saved by converting a portion of the fluid power that isnot demanded by the load into a corresponding reduction in the demand onthe prime mover.

Although the displacers 36 and 38 operate quite efficiently, thesecondary pressure line 24 is used to by-pass the two displacers whenfull flow from the fixed displacement pump 10 is demanded by the load.However, when either displacer is used as a motor for driving the otheras a pump, pressure in the secondary pressure line 24 is reduced withrespect to pressure in the system output line 30, and the full flow fromthe fixed displacement pump 10 is directed through the displacers viasecondary pressure line 26. The check valve 28 prevents a reversal offluid flow in the secondary pressure line 24 from the system output line30. The check valves 48 and 50 prevent a similar reversal of fluid flowin the respective pressure lines 40 and 42 when one of the valves 56 and58 is opened.

FIG. 2 illustrates another example of a pumping system in which myregenerator is used to save energy. However, the primary pump of thisexample is formed by mechanically connecting a pair of displacers 66 and68 to each other and to a prime mover 70. A primary intake line 72,which draws fluid from a vented reservoir 74, branches into twosecondary intake lines 76 and 78 that connect to respective input ports80 and 82 of the displacers. Check valves 84 and 86 prevent fluid in thesecondary intake lines from returning to the reservoir 74.

Pressure lines 88 and 90 extend through respective check valves 92 and94 and connect respective output ports 96 and 98 of the displacers to asystem output line 100. Return lines 102 and 104, interrupted by a firstpair of shutoff valves 106 and 108, connect the respective pressurelines 88 and 90 to the reservoir 74. The shutoff valves 106 and 108 arebiased to open positions for reasons noted above but can be switched toclosed positions by respective solenoid actuators.

A primary feedback line 110 is connected to the system output line 100and branches into two secondary feedback lines 112 and 114 that arerespectively joined to the secondary intake lines 76 and 78. A secondpair of similarly operated shutoff valves 116 and 118 respectivelyinterrupt the secondary feedback lines 112 and 114 to control fluid flowfrom the system output line 100 to the input port of one or the other ofthe displacers 66 and 68.

Controller 120 is arranged to receive information from pressure sensor122 and to control the operating positions of the shutoff valves 106,108, 116, and 118 for at least approximately matching output flow fromthe displacers to the demand for fluid flow by a load. Differentcombinations of the valve operating positions are used to selectivelyoperate the displacers as pumps, motors, or recirculators forincrementally varying the collective output flow of the displacers.

For example, FIG. 2 depicts the valve operating positions that arerequired for operating the displacer 66 as a pump and the displacer 68as a motor. In particular, valve 106 is closed to direct output flowfrom the displacer 66 to the system output line 100, and the valve 108is open to return output flow from the displacer 68 to the reservoir 74.The valve 116 is also closed to prevent any of the output flow to thesystem output line 100 from being recirculated to the displacer 66, butvalve 118 is open to feed back a portion of the output flow from thedisplacer 66 (the larger of the two displacers) to the input port 82 ofthe displacer 68.

Part of a pressurized flow produced by displacer 66 operating as a pumpis used to drive the displacer 68 as a motor for reducing power demandson the prime mover 70. Since the displacer 68 operating as a motor isdriven by part of the output flow of the other displacer 66 operating asa pump, the output flow to the load is determined by subtracting theflow through the displacer 68 from the flow through the displacer 66.The reduction in flow is converted into an energy savings in two ways.First, by not operating the displacer 68 as a pump, demand on the primemover 70 for driving the displacers is reduced. Second, by operating thedisplacer 68 as a motor, a portion of the fluid power produced by thedisplacer 66 operating as a pump is converted into mechanical power thatfurther reduces the demand on the prime mover to a fraction of the powerrequired to drive the displacer 66.

Alternatively, the displacer 68 can be switched from operating as amotor to operating as a recirculator by closing either of the valves 108and 118. If the valve 108 is closed, a constant volume of fluid isrecirculated between input and output ports of displacer 68. If thevalve 118 is closed instead, the displacer 68 recirculates fluid to andfrom the reservoir. However, closing either valve 108 or 118 increasesfluid flow in the system output line 100 to the full output flow of thedisplacer 66. As a recirculator, operation of the displacer 68 does notadd any significant demand to the prime mover 70 beyond the requirementsfor driving the displacer 66.

FIG. 3 is a composite illustration of several ways in which myregenerator can be used with a fluid actuator to save energy. Forexample, the depicted fluid flow network provides for effectivelyconfiguring the regenerator to control flow rates either into or out ofthe actuator. Although depicted as a fixed displacement motor 124, theactuator could also be another type of load device such as a fluidcylinder that converts fluid power into mechanical force and linearmotion.

The fixed displacement motor 124 is supplied with fluid power from apressure line 126 that extends from a source of fluid flow (not shown).Two-position valves 128 and 130 interrupt fluid flow in the pressureline 126 to the fixed displacement motor 124. An alternative pressureline 132, interrupted only by shutoff valve 133, by-passes the shutoffvalves 128 and 130 and the fixed displacement motor 124 and connects toa primary exhaust line 134 of the fixed displacement motor.

The primary exhaust line 134 connects to respective input ports 136 and138 of displacers 140 and 142, which are mechanically coupled to eachother. Output ports 144 and 146 of the displacers connect to respectivesecondary exhaust lines 148 and 150 that extend through respective checkvalves 152 and 154. The two secondary exhaust lines 148 and 150 arejoined together with a feedback line 156 that connects to the pressureline 126 between shutoff valve 128 and shutoff valve 130. The feedbackline 156 is interrupted by both a shutoff valve 158 and a check valve160. The shutoff valve 158 forms part of a so-called "power beyond"circuit 162 that diverts regenerated fluid power through intermediateline 164 to another actuator or fluid power system (neither of which isshown), or the fluid power could be similarly diverted to an input portof a pump (also not shown) supplying a flow of fluid to the pressureline 126. The check valve 160 prevents fluid in the pressure line 126from reversing flow in the feedback line 156.

A shutoff valve 166 interrupts the primary exhaust line 134 between thefixed displacement motor 124 and the alternative pressure line 132.Between the fixed displacement motor 124 and the shutoff valve 166, areturn line 168, interrupted by shutoff valve 170, connects the primaryexhaust line 134 to a vented reservoir 172. Similarly, return lines 174and 176, interrupted by respective shutoff valves 178 and 180, connectrespective secondary exhaust lines 148 and 150 to the reservoir 172. Anintake line 182 connects the reservoir 172 to a portion of the pressureline 126 between the shutoff valve 130 and the fixed displacement motor124. Check valve 184, located along the intake line 182, prevents fluidflow to the reservoir 172.

The fixed displacement motor 124 is partly controlled by athree-position directional control valve 186 that interconnects thepressure line 126 and the primary exhaust line 134 with feed lines 188and 190 to respective motor ports 192 and 194. The three-position valve186 allows the fixed displacement motor to be driven in eitherdirection.

A controller 196 is arranged to control combinations of motor rotationalspeed and torque as well as a degree of fluid flow resistance forbraking the motor. The controller 196 receives information from pressuresensors 198 and 200 respectively located along pressure line 126 andprimary exhaust line 134 and a flow rate sensor 202 also located alongthe pressure line 126. All of the shutoff valves shown in FIG. 3 arebiased to open positions but can be switched to closed positions byrespective solenoid actuators that are energized in various combinationsby the controller 196.

For example, output flow from the fixed displacement motor 124 can becontrolled by closing valve 133 in the alternative pressure line 132,valve 170 in the return line 168, and either one of the valves 178 and180 in the respective return lines 174 and 176. Assuming closure ofvalve 180, the displacer 140 is operated as a motor by remaining fluidpressure in the primary exhaust line 134, and the displacer 142 isoperated as a pump that is driven by the displacer 140. The displacer142 operating as a pump discharges a flow of pressurized fluid intofeedback line 156 that either returns the flow to pressure line 126 ordiverts the flow to the power beyond circuit 162 by closing valve 158.

Fluid flow to the fixed displacement motor 124 is controlled in asimilar manner by closing valve 128 in the pressure line 126, valve 166in the primary exhaust line 134, and either one of the valves 178 and180 in the respective return lines 174 and 176. Assuming closure ofvalve 180, the displacer 140 is operated as a motor by fluid pressure inthe alternative pressure line 132, and the displacer 142 is operated asa pump that is driven by the displacer 140. The displacer 142 operatingas a pump discharges a flow of pressurized fluid into feedback line 156that returns the flow to pressure line 126 for driving the fixeddisplacement motor 124.

The arrangement of my regenerator for controlling flow from the fixeddisplacement motor 124 is particularly suitable for extending the usualoperating range of the motor to include low torque but high rotationalspeed operation. For example, fluid fed back to the pressure line 126can be used to increase the flow rate to the motor. In contrast, thearrangement of my regenerator for controlling flow to the fixeddisplacement motor 124 is particularly suitable for extending the usualoperating range of the motor to include high torque but low rotationalspeed operation. For example, the portion of the fluid flow that is notreturned to the pressure line 126 can be used to further pressurize theremaining fluid flow to the motor.

An arrangement of my regenerator similar to the arrangement forcontrolling flow from the fixed displacement motor 124 can also be usedto brake the motor, while returning energy expended to brake the motoras a flow of pressurized fluid. In addition to closing the valvesrequired to control flow from the fixed displacement motor, valve 130 inpressure line 126 is also closed to isolate the motor from the source ofpressurized fluid. Momentum enables the motor to operate temporarily asa pump that draws fluid from the reservoir 172 through intake line 182.The discharge from the fixed displacement motor operating as a pump ishandled in a manner similar to the arrangement for controlling flow fromthe fixed displacement motor. However, valve 130 prevents any of theflow fed back to the pressure line 126 from reaching the motor.

FIG. 4 illustrates another example of a motor system in which myregenerator is used to save energy. However, a motor in this example isformed by mechanically connecting a pair of displacers 204 and 206 to aload 208.

A primary pressure line 210 from a source of fluid flow (not shown)branches into two secondary pressure lines 212 and 214 that areinterrupted by respective shutoff valves 216 and 218. The secondarypressure lines 212 and 214 connect to respective input ports 220 and 222of the displacers 204 and 206. Output ports 224 and 226 of the twodisplacers are connected to respective exhaust lines 228 and 230 thatextend through check valves 232 and 234. The two exhaust lines 228 and230 join together with a feedback line 236 that connects to primarypressure line 210.

Intake lines 238 and 240 connect a vented reservoir 242 to therespective secondary pressure lines 212 and 214 through check valves 244and 246. Return lines 248 and 250, interrupted by shutoff valves 252 and254, connect the respective exhaust lines 228 and 230 to the reservoir242.

Controller 256 is arranged to control the operating positions of theshutoff valves 216, 218, 252, and 254 for at least approximatelymatching the consumption of fluid power to the demand for rotationalspeed and torque of the load. Different combinations of the valveoperating positions are used to selectively operate the displacers 204and 206 as pumps, motors, or recirculators for incrementally varying themechanical and fluid power output of the displacers.

For example, FIG. 4 depicts valves 218 and 254 in closed positions tooperate displacer 204 as a motor and displacer 206 as a pump. Thedisplacer 204 operating as a motor drives both the load 208 and thedisplacer 206 as a pump. Fluid power that is not required to drive theload 208 is used by the displacer 206 operating as a pump to drawadditional fluid from the reservoir 242 and to add the additional fluidto the flow of the primary pressure line 210. Although not shown, theadditional fluid flow could also be diverted to a "power beyond" circuitsuch as shown in FIG. 3 or to an input port of a pump supplying a flowof fluid to the pressure line 210.

A more detailed example of my regenerator used in conjunction with afixed displacement pump is shown in FIG. 5 in which two gangs ofdisplacers are arranged within a fluid flow network as a furtherdevelopment of the first basic configuration shown in FIG. 1. Similar tothe earlier-described configuration, a fixed displacement pump 260driven by a prime mover 262 draws fluid from a vented reservoir 264through an intake line 266 and outputs a flow of fluid into a primarypressure line 268.

The fluid flow network begins with secondary pressure lines 270 and 272that branch from the primary pressure line 268. The secondary pressureline 270 extends through a check valve 274 and connects directly to asystem output line 276. The secondary pressure line 272 connects torespective input ports of a first gang of displacers 278 that areindividually labeled in upper case characters "A", "B", and "C". Outputports of the same displacers are connected to respective tertiarypressure lines 280, 282, and 284 for dividing the fluid flow intopredetermined proportions.

The tertiary pressure line 280 connects to respective input ports of asecond gang of displacers 286 that are individually labeled in lowercase characters "a", "b", "c", and "d". The other tertiary pressurelines 282 and 284 extend through respective check valves 288 and 290 andjoin together with the secondary pressure line 270. Secondary returnlines 292 and 294 connect the respective tertiary pressure lines 282 and284 to a primary return line 296 that empties into the reservoir 264.Shutoff valves 298 and 300 interrupt the respective secondary returnlines 292 and 294 to control fluid flow from the respective tertiarypressure lines 282 and 284 to the reservoir 264.

Output ports of the second gang of displacers 286 connect to respectivequaternary pressure lines 302, 304, 306, and 308 that extend throughrespective check valves 310, 312, 314, and 316 and join together withthe system output line 276. The quaternary pressure lines 302, 304, 306,and 308 also branch into respective secondary feedback lines 318, 320,322, and 324 and respective secondary return lines 326, 328, 330, and332.

The secondary feedback lines 318, 320, 322, and 324 extend throughrespective check valves 342, 344, 346, and 348 and join together with aprimary feedback line 350 that connects to the tertiary pressure line280. Shutoff valves 334, 336, 338, and 340 interrupt the secondaryfeedback lines 318, 320, 322, and 324 to control a recirculation offluid from the quaternary pressure lines 302, 304, 306, and 308 to thetertiary pressure line 280. The secondary return lines 326, 328, 330,and 332 connect the quaternary pressure lines 302, 304, 306, and 308 tothe primary return line 296. Shutoff valves 352, 354, 356, and 358interrupt the secondary return lines 326, 328, 330, and 332 to controlfluid flow from the respective quaternary pressure lines 302, 304, 306,and 308 to the reservoir 264.

Another secondary return line 360 connects the tertiary pressure line280 to the primary return line 296. An adjustable pressure compensatedflow control valve 362, hereinafter referred to as a "modulating valve",interrupts the secondary return line 360 to regulate fluid flow from thetertiary pressure line 280 to the reservoir 264. All ten of the shutoffvalves identified in this example are actuated by solenoids but arebiased into open positions to protect the fluid flow network againstdamage accompanying an electrical failure.

The two different gangs of displacers 278 and 286 are used toaccommodate a much larger range of fluid flow rates and to adapt myregenerator to different size systems. The first gang of displacers 278directs a predetermined portion of the fluid flow from fixeddisplacement pump 260 to the second gang of displacers 286. Theremaining fluid flow through the first gang of displacers is dividedbetween the system output line 276 and the reservoir 264. However, anyof the fluid that is allowed to pass through the shutoff valves 298 and300 to the reservoir 264 drives one or both of the displacers "B" or "C"as a motor. The other mechanically connected displacers, includingdisplacer "A", can be driven as pumps for converting fluid power in thereturn flow into useful work reducing output pressure of the pump 260.

The first gang of displacers 278 is arranged with individual displacersthat are sized to divide the fluid flow between the pressure and returnlines into increments corresponding to multiples of the fluid flowthrough displacer "A" to the second gang of displacers 286. For example,the displacers "A", "B", and "C" can be sized in respective proportions:1, 1, and 2 for dividing the flow into four increments, each covering adifferent twenty-five percent portion of the flow to the system outputline 276. The remaining portions of the flow that are returned to thereservoir 264 are regenerated. The table below shows how the displacers"B" and "C" are operated within the fluid flow network to regeneratepower from different proportions of the output flow from the fixeddisplacement pump 260, where "M" represents "motor" and "P" represents"pump".

    ______________________________________                                        OPERATION      PERCENT                                                        B            C     REGENERATED                                                ______________________________________                                        P            P      0%-25%                                                    M            P     25%-50%                                                    P            M     50%-75%                                                    M            M      75%-100%                                                  ______________________________________                                    

Up to twenty-five percent of the fluid flow in the secondary pressureline 272 can also be regenerated by the second gang of displacers 286,and this accounts for the twenty-five percent range associated with eachof the listed operating states of the displacers "B" and "C". Withineach twenty-five percent range, the displacer "A" operates as either apump or a motor depending upon pressure differences between thesecondary pressure line 272 and the tertiary pressure line 280.

For example, when both of the shutoff valves 298 and 300 are closed,limiting operation of the displacers "B" and "C" as pumps, any of theflow regenerated by the second gang of displacers 286 lowers pressure inthe tertiary pressure line 280 with respect to the secondary pressureline 272 and drives displacer "A" as a motor. The displacers "B" and "C"are driven by the displacer "A" as pumps for proportionally lowering thepressure in the secondary pressure line 272 as well as the primarypressure line 268.

In contrast, when one or the other of the shutoff valves 298 and 300 isopen for operating one of the respective displacers "B" and "C" as amotor, the pressure in the tertiary pressure line 280 can be more orless than the pressure in the secondary pressure line 272. This relativepressure fluctuation relates to the amount of regeneration practiced bythe second gang of displacers 286. Accordingly, the displacer "A" can beoperated either as a pump for decreasing pressure in the secondarypressure line 272 or as a motor for helping to drive one of the otherdisplacers "B" and "C" as a pump. However, when the shutoff valves 298and 300 are open for operating both of the displacers "B" and "C" asmotors, the displacer "A" is driven as a pump for reducing pressure inthe secondary pressure line 272 with respect to the pressure in thetertiary pressure line 280.

However, unless at least one displacer of either gang of displacers 278or 286 operates as a motor, the fluid flow from the fixed displacementpump by-passes both gangs of displacers along secondary pressure line270 as a path of least resistance. However, if either of the gangs ofdisplacers is operated for regenerating a portion of the fluid flow(i.e., at least one of the displacers is used as a motor), then theoutput pressure of the fixed displacement pump 260 is reduced withrespect to the pressure in the system output line 276. Check valve 274prevents backflow from the system output line 276 to the reducedpressure output flow of the fixed displacement pump 260.

The second gang of displacers 286 is arranged to further divide aportion of the fluid flow in tertiary pressure line 280 into finerincrements. Output flows from each of the displacers "a", "b", "c", and"d" can be directed to the system output line 276, combined with thefluid flow in the tertiary pressure line 280, or returned to thereservoir 264. The displacers whose output flow is returned to thereservoir function as motors; the displacers whose output flow iscombined with the flow in the tertiary pressure line 280 function asrecirculators; and the remaining displacers whose output flow isdirected to the system output line function as pumps. The displacersoperating as motors provide mechanical power for driving other of thedisplacers as pumps. The displacers operating as recirculators requirethe remaining displacers to accommodate larger proportions of the fluidflow in the tertiary pressure line 280.

The displacers are sized to divide the fluid flow in the tertiarypressure line 280 into even increments that number more than thedisplacers. For example, the displacers "a", "b", "c", and "d" can besized in respective proportions: 1, 3, 6, and 10 for dividing the fluidflow in tertiary pressure line 280 into twenty increments, each coveringa different five percent interval of the flow. However, five percent ofthe flow in tertiary pressure line 280 actually corresponds to one andone-quarter percent of the output flow from the fixed displacement pump260 (i.e., five percent of twenty-five percent). Thus, the two gangs ofdisplacers operating together divide the fluid flowing through myregenerator into eighty parts (i.e., twenty times four).

The following table shows how the displacers "a", "b", "c", and "d" areoperated within the fluid flow network to regenerate differentproportions of the fluid flow in the tertiary pressure line 280, where"M" represents "motor", "P" represents "pump", and "R" represents"recirculator".

    ______________________________________                                        OPERATION          PERCENT                                                    a       b        c       d   REGENERATED                                      ______________________________________                                        M       P        P       P    5%                                              M       P        P       R   10%                                              P       M        P       P   15%                                              M       M        P       P   20%                                              M       P        R       R   25%                                              P       P        M       P   30%                                              M       P        M       P   35%                                              M       M        P       R   40%                                              P       M        M       P   45%                                              M       M        M       P   50%                                              M       P        P       M   55%                                              P       P        M       R   60%                                              P       M        P       M   65%                                              M       M        P       M   70%                                              P       M        R       R   75%                                              P       P        M       M   80%                                              M       P        M       M   85%                                              P       M        M       R   90%                                              P       M        M       M   95%                                              ______________________________________                                    

None (zero percent) of the flow through tertiary pressure line 280 isregenerated by closing all of the shutoff valves 352, 354, 356, and 358in the respective secondary return lines 326, 328, 330, and 332. Thefluid flow passes through the displacers "a", "b", "c", and "d" withoutany change in pressure to the system output line 276. Alternatively, allof the fluid flowing in the tertiary pressure line 280 can be directedthrough the secondary return lines 326, 328, 330, and 332, whichcollectively exhaust displacer "A" of the first group of displacers 278to the reservoir 264; and this has the effect of regenerating all (onehundred percent) of the flow in the tertiary pressure line 280.

The modulating valve 362 interrupting the secondary return line 360 isused to more exactly control the flow rate in the system output line 276that is required to maintain a desired system pressure. In other words,desired flow rates that fall between the one and one-quarter percentincrements provided by controlling fluid flow through the two gangs ofdisplacers 278 and 286 are achieved by exhausting very small portions ofthe fluid flow (i.e., portions less than the one and one-quarterpercent) to the reservoir 264. The corresponding energy losses are alsovery small, but are made even smaller by exhausting fluid from thetertiary pressure line 280 through the secondary return line 360 to thereservoir 264.

For instance, pressure in the tertiary pressure line 280 varies betweenzero and system pressure depending upon the percent of the flow in thetertiary line 280 that is subsequently exhausted through the secondaryreturn lines 326, 328, 330, and 332 to the reservoir 264. Accordingly,the average pressure in the tertiary pressure line 280 is expected to beabout one-half of the system pressure. Thus, the average energy lossaccompanying fluid flow through the modulating valve 362 is also reducedby one-half with respect to energy loss associated with exhausting thesame volume of fluid at the system pressure.

FIGS. 6 and 7 depict details of two special control systems that arearranged to control the operation of my regenerator shown in FIG. 5.More particularly, FIG. 6 depicts details of an electronic controlsystem that senses both pressure and flow rate in the system output line276 (shown also in FIG. 5) and responds to changes in the sensedconditions by actuating various combinations of the ten shutoff valvesshown in FIG. 5 and by regulating operation of the modulating valve 362shown in the same figure.

A pressure sensor 364 and a flow rate sensor 366 connect to the systemoutput line 276 and deliver respective signals 368 and 370 to aprogrammable controller 372 that is preferably arranged as a so-called"proportional integral derivative controller". The signals 368 and 370allow the programmable controller 372 to monitor pressure and flow ratein the system output line 276. An accumulator 374, charged with fluid atsystem pressure, momentarily compensates for any change in the flow raterequired to satisfy a demand of a load 376 that is supplied with fluidat the system pressure.

Each of the incremental divisions at which my regenerator is setcorresponds to a different percentage of a predetermined flow rate fromthe fixed displacement pump 260 (shown in FIG. 5). The modulating valve362 is set to regulate flow rates between each of the incrementaldivisions. This information, along with a desired or "set point" systempressure, is input to the programmable controller 372 by an input signal378. The programmable controller 372 periodically compares the monitoredflow rate with a flow rate at which my regenerator is set and, based ona difference between these two values, determines a new setting of myregenerator to exactly match the monitored flow rate.

Control signals 380 and 382 communicate the new setting of myregenerator to respective drivers 384 and 386 for the ten shutoff valvesand the modulating valve 362. The driver 384 includes a sequence decoderfor translating the output signal 380 into individual open or closedsettings of each of the shutoff valves. A first group of output signals388 from the driver 384 controls the solenoid actuation of shutoffvalves 298 and 300 in the secondary return lines from the displacers "B"and "C". A second group of output signals 390 controls the solenoidactuation of shutoff valves 352, 354, 356, and 358 in the secondaryreturn lines from the displacers "a", "b", "c", and "d". A third groupof output signals 392 controls the solenoid actuation of shutoff valves334, 336, 338, and 340 in the feedback lines from the same displacers"a", "b", "c", and "d". In addition, output signal 394 from the driver386 controls operation of the modulating valve 362 for more closelymatching the output flow from my regenerator to the monitored flow ratedemand momentarily accommodated by the accumulator 374.

Although my regenerator is arranged to closely match the flow ratedemand of the load 376, small differences between the actual and thedemanded flow rates tend to accumulate in the form of a change in thesystem pressure. In other words, the system pressure can drift eitherabove or below the set point pressure. However, the programmablecontroller monitors the pressure in the system output line 276 andcompares the monitored pressure with the set point pressure to determinean appropriate remedial change in the regenerator settings for limitingsuch deviations in the system pressure. The remedial changes in settingsare superimposed upon the settings that are determined to satisfy thedemanded flow rate and are generally made by merely adjusting thesetting of the remedial valve.

Thus, instead of merely reacting to changes in system pressure, myelectronic control system reacts primarily to changes in demanded flowrate for greatly reducing the fluctuations in system pressure requiringfurther correction. Also, the control system provides for making largechanges in flow rate to accommodate sudden changes in flow demand withlittle or no change to the system pressure.

An alternative fluid powered control system is depicted in FIG. 7 forcontrolling the operation of my regenerator shown in FIG. 5. The fluidpowered control system requires several different connections to thepumping system, and these connections are illustrated by showing detailsof the pumping system including the location of the fluid flow network396 of my regenerator.

The fixed displacement pump 260 powered by the prime mover 262 drawsfluid from the reservoir 264 through intake line 266 and outputs thefluid at a fixed flow rate through primary pressure line 268 andsecondary pressure line 272. An adjustable flow control valve,hereinafter referred to as a "flow restricting valve", is adjusted toproduce a small amount of backpressure against the fixed displacementpump. Differential pressure across the flow restricting valve 398 iscommunicated to a double-acting cylinder 400 by pressure control lines402 and 404 and urges the cylinder plunger together with double-endedrod 406 in the direction of arrow 408.

A control line 410 connected to the system output line 276 branches intoflow control line 412 and pressure control line 414. Flow restrictingvalve 416 in the flow control line 412 is adjusted with respect to flowrestricting valve 418 in the pressure control line 414 to offer slightlyless resistance to fluid flow. The pressure control line 414 connects toopposite ends of a double-acting cylinder 420 having a plunger with asingle end rod 422 that is connected to the double-ended rod 406 ofdouble-acting cylinder 400. The single end rod 422 effectively reducesarea on one side of its attached plunger, and this produces adifferential force that urges the plunger and the single end rod 422 inthe direction of arrow 424.

A rack 426 having a number of detents 428 is also attached to thedouble-ended rod 406 so that the rack 426 moves together with both rods406 and 422. The two double-acting cylinders are sized to exert linearforces with their respective rod ends that counteract each other whenfluid in the system output line 276 is at the system set point pressure.However, if the system pressure decreases below the set point pressure,the force exerted by the double-acting cylinder 400 prevails, and therack 426 is moved in the direction of arrow 408. Conversely, if thesystem pressure increases above the set point pressure, the forceexerted by the double-acting cylinder 420 prevails, and the rack 426 ismoved in the direction of arrow 424.

Movement of the rack 426 in either direction operates a set of pilotvalves 430 that are used to selectively actuate the shutoff valves shownin FIG. 5. (Although depicted with solenoid actuators, the shutoffvalves can also be made with conventional pressure-responsive actuatorsthat can be controlled by pilot valves.) Although only five pilot valves430 are depicted in FIG. 7, the number of pilot valves is intended tomatch the number of shutoff valves used in my regenerator. The detents428 are spaced in the rack 426 with respect to the pilot valves 430 toprogressively increase or decrease flow rate through my regenerator inresponse to relative movement of the rack 426 in opposite directions.The excess flow drains to the reservoir 264 through primary return line296.

The pilot valves are carried from opposite ends of double-ended rod 432of a spring-centered, double-acting cylinder 434. Secondary flow controllines 436 and 438 connect opposite ends of the double-acting cylinder434 to flow control line 412, which terminates at an accumulator 440charged with fluid at the system pressure. A flow restricting valve 442is adjusted to permit small rates of fluid flow to and from theaccumulator to pass without significant resistance. However, largerrates of flow to and from the accumulator are restricted, producingdifferential pressures at the opposite ends of the double-actingcylinder 434. Increases in flow demand move the double-ended rod 432together with the pilot valves 430 in the direction of arrow 444,whereas decreases in flow demand move the double-ended rod 432 togetherwith the pilot valves 430 in the direction of arrow 446. Althoughsensitive to changes in flow rate rather than pressure, these relativemovements of the pilot valves 430 with respect to the rack 426 alsoprovide for controlling operation of the shutoff valves to progressivelyincrease or decrease flow rate through my regenerator.

The flow restricting valves 416 and 418 control sensitivity of thecontrol system between changes in flow rate and pressure. Preferably,the flow restricting valve 418 offers more resistance to fluid flow thanthe flow restricting valve 416 so that the system reacts more quickly tochanges in flow rate. However, changes in flow rate and pressure producecompound movement between the pilot valves 430 and the rack 426, andthis compound movement further decreases reaction time of the controlsystem.

More generally, my regenerator is controlled to divide a flow of fluidinto two relatively variable sized portions. One portion is sized tosatisfy a particular demand for fluid flow, and the remaining portion ofthe flow is converted into useful work. The division of flow can be usedto replace the functions of valves or other devices for regulatingpressure or flow rate. Available fluid power that is not required tosatisfy a particular demand for a given pressure or flow rate is firsttransformed into mechanical power by driving one or more of a gang ofdisplacers as a motor. The mechanical power generated by the displacersoperating as motors is used to drive other of the displacers as pumps.The displacers operating as pumps accomplish useful work either byreducing differential pressure across a primary pump driven by a primemover or by contributing an additional flow of fluid.

A first regenerator configured for use in a fluid pumping system canalso be used together with a second regenerator configured for use witha fluid actuating system. This saves energy throughout fluid powersystems. Also, the gangs of displacers of my regenerators that are usedin conjunction with fixed displacement pumps and motors can also beprovided with separately accessible inputs to their individualdisplacers similar to my regenerators that can be used in place ofvariable displacement pumps and motors. In this way, displacersoperating as motors can be used to subtract from the output ofdisplacers operating as pumps to provide further divisions of the fluidflow through the gangs of displacers. My regenerator can also beconstructed as an integrated circuit by forming the lines of the fluidflow network as passages in an integral block of material.

The selectable flow paths of the fluid flow network are preferablylimited to a common direction through the displacers so that thedisplacers can be rotated in unison. The displacers of each gang arealso preferably made as gear drives having one gear member of each drivecoupled to a common shaft. The different proportions into which the geardrives divide the flow of fluid relate to relative face widths of therespective gear members of the drives. The gear drives are preferredbecause they are very rugged and reliable. However, other fixeddisplacement devices including vane and piston drives could be used inplace of the gear drives.

My regenerator is expected to be especially useful for improvingefficiencies of so-called "mobile hydraulic" units powered by vehicleengines. For example, my regenerator can provide substantial powersavings in fluid power systems for steering vehicles or liftingimplements.

I claim:
 1. A regenerator for use in a system conveying fluid power as aflow of fluid under pressure to a load comprising:a gang of fixed sizedisplacers that are mechanically connected to each other for displacingpredetermined portions of the flow of fluid; a fluid flow networkincorporating said gang of displacers within an array of selectable flowpaths through said displacers; a control system responsive to changes indemand for fluid power by the load for selecting among said flow pathsto transform varying portions of the fluid power conveyed by the flow offluid into mechanical power conveyed between the displacers; said fluidflow network including: first and second displacers of said gang ofdisplacers having respective input and output ports, a first pressureline for connecting said input ports of the first and second displacersto a source of the flow of fluid, a second pressure line for connectingsaid output ports of the first and second displacers to the load, and areturn line for connecting said output port of the first displacer to astore of the fluid; said control system is arranged for responding to adecreased demand for fluid power in said second pressure line bydiverting fluid flowing out of said output port of the first displacerfrom said second pressure line to said return line; said first displacerconnecting said first pressure line to said return line is arranged forbeing driven as a motor for driving said second displacer connectingsaid first pressure line to said second pressure line as a pump; saidsecond displacer is arranged for being driven as a pump for reducingpressure in said first pressure line with respect to said secondpressure line; and said fluid flow network also including: a thirddisplacers of said gang of displacers having an input port and an outputport, said first pressure line also providing for connecting said inputport of the third displacer to the source of the flow of fluid, saidsecond pressure line also providing for connecting said output port ofthe third displacer to the load, said return line also providing forconnecting said output port of the third displacer to the store offluid, and a feedback line for connecting said output port of the thirddisplacer to said first pressure line.
 2. The regenerator of claim 1 inwhich said control system further provides for diverting fluid flowingout of said output port of the third displacer from said second pressureline to one of said return line and said feedback line.
 3. Theregenerator of claim 2 in which said third displacer connecting saidfirst pressure line to said feedback line operates as a recirculator foreffectively removing said third displacer from the flow of fluid and fordividing the flow of fluid among said first displacer operating as amotor and said second displacer driven as a pump.
 4. A fluid powerregenerator for saving energy in a fluid pumping system having a fixeddisplacement pump that draws fluid from a reservoir for providing a flowof fluid under pressure to a load comprising:first and second displacersthat are mechanically interconnected with each other independently ofthe fixed displacement pump for dividing the flow of fluid intopredetermined proportions; a first pressure line operating at a firstfluid pressure for connecting an output port of the fixed displacementpump to respective input ports of said first and second displacers; asecond pressure line operating at a second fluid pressure for connectingrespective output ports of said first and second displacers to the load;a return line for connecting said output port of the first displacer tothe reservoir; a valve for alternatively connecting said output port ofthe first displacer to one of said second pressure line and said returnline; a sensor for monitoring the second fluid pressure in said secondpressure line; a control system for comparing the second fluid pressureto a desired pressure and for determining changes in a rate of fluidflow to the load required to maintain the second fluid pressure at thedesired pressure; and p1 said control system including a logic networkcontrolling operation of said valve for connecting said output port ofthe first displacer to said return line in response to the second fluidpressure being greater than the desired pressure to reduce both the rateof fluid flow to the load and the first fluid pressure in said firstpressure line.
 5. The fluid power regenerator of claim 4 in which saidfirst displacer connecting said first pressure line to said return lineis driven as a motor for reducing the rate of fluid flow to the load atthe desired pressure and for driving said second displacer connectingsaid first pressure line to said second pressure line as a pump.
 6. Thefluid power regenerator of claim 4 in which said second displacer drivenas a pump reduces the first fluid pressure in said first pressure linewith respect to the desired pressure for more closely matching poweroutput of the fixed displacement pump with a reduced demand for fluidpower by the load.
 7. The fluid power regenerator of claim 6 furthercomprising an accumulator for momentarily satisfying the demand for theflow of fluid to the load at the desired pressure and another sensor formonitoring the rate of fluid flow that is required to maintain thedesired pressure.
 8. The fluid power regenerator of claim 7 in whichsaid control system also compares the monitored rate of fluid flow torates of fluid flow expected from the operation of said valve for morerapidly matching the demand for fluid power from the load.
 9. A fluidpumping system for supplying a flow of fluid at a constant pressure to aload comprising:a fixed displacement pump operable by a prime mover forproducing the flow of fluid; first and second displacers that aremechanically interconnected with each other independently of said fixeddisplacement pump for dividing the flow of fluid into predeterminedproportions; an intake line connecting an input port of said fixeddisplacement pump to a reservoir; a first pressure line connecting anoutput port of said fixed displacement pump to respective input ports ofsaid first and second displacers; a second pressure line connectingrespective output ports of said first and second displacers to the load;a return line connecting said output port of the first displacer to thereservoir; a valve for alternatively connecting said output port of thefirst displacer to one of said second pressure line and said returnline; said first displacer connecting said first pressure line to saidreturn line is arranged for being driven as a motor for driving saidsecond displacer connecting said first pressure line to said secondpressure line as a pump; said second displacer is arranged for beingdriven as a pump for reducing pressure in said first pressure line withrespect to said second pressure line; and a modulating valveinterrupting a second return line that connect said first pressure lineto said reservoir.
 10. A method of regenerating a portion of a flow offluid between a fixed displacement pump and a load comprising the stepsof:directing the flow of fluid within a fluid flow network through agang of fixed size displacers that divide the flow of fluid intopredetermined proportions; diverting a portion of the fluid flow througha first number of displacers form the load to a reservoir for drivingthe first number of displacers as motors and for reducing the flow offluid to the load to reduce an outlet fluid pressure within the fluidflow network between the displacers and the load; driving a secondnumber of the remaining displacers as pumps with mechanical powergenerated by the first number of displacers operating as motors forreducing an inlet fluid pressure between the fixed displacement pump andthe displacers; and controlling the diversion of fluid flow throughdifferent numbers of the displacers operating as motors for reducing theinlet fluid pressure to more closely match output power of the fixeddisplacement pump with a reduced demand for fluid power by the load. 11.The method of claim 10 further comprising the steps of:monitoring theoutlet fluid pressure; comparing the outlet fluid pressure to a desiredfluid pressure; and determining changes is the rate of fluid flow to theload required to maintain the outlet fluid pressure at the desiredpressure.
 12. A method of regenerating a portion of a flow of fluidbetween a source of the flow of fluid and a load comprising the stepsof:directing the flow of fluid within a fluid flow network through agang of fixed size displacers that divide the flow of fluid intopredetermined proportions; diverting a portion of the fluid flow througha first number of the displacers from the load to a reservoir fordriving the first number of displacers as motors; driving a secondnumber of the remaining displacers as pumps with mechanical powergenerated by the first number of displacers operating as motors;controlling the diversion of fluid flow through different numbers of thedisplacers operating as motors for varying a rate of fluid flow to theload; said step of controlling the diversion of fluid flow includingdividing the flow of fluid between the load and the reservoir inincremental divisions that number more than a total number of thedisplacers; and controlling a valve to further vary the rate of fluidflow to the load between the incremental divisions of the flow of fluidcontrolled by the diversion of fluid flow through different displacers.